U.S. patent application number 15/190687 was filed with the patent office on 2017-12-28 for hydraulic fracturing in kerogen-rich unconventional formations.
The applicant listed for this patent is Saudi Arabian Oil Company. Invention is credited to Younane N. Abousleiman, Yanhui Han, Katherine Leigh Hull, David Jacobi, Leiming Li, Ghaithan Muntasheri.
Application Number | 20170370197 15/190687 |
Document ID | / |
Family ID | 59091663 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170370197 |
Kind Code |
A1 |
Han; Yanhui ; et
al. |
December 28, 2017 |
Hydraulic Fracturing In Kerogen-Rich Unconventional Formations
Abstract
The subject matter of this specification can be embodied in,
among other things, a method for treating a geologic formation that
includes providing a hydraulic fracture model, providing a first
value representative of a volume of kerogen breaker in a fracturing
fluid, determining a discrete fracture network (DFN) based on the
hydraulic fracture model and the first value, determining a
geomechanical model based on the DFN and a reservoir model based on
the DFN, determining a hydrocarbon production volume based on the
geomechanical model and the reservoir model, adjusting the first
value based on the hydrocarbon production volume, and adjusting a
volume of kerogen breaker in the fracturing fluid to a hydrocarbon
reservoir based on the adjusted first value.
Inventors: |
Han; Yanhui; (Katy, TX)
; Li; Leiming; (Sugar Land, TX) ; Muntasheri;
Ghaithan; (Katy, TX) ; Abousleiman; Younane N.;
(Norman, OK) ; Hull; Katherine Leigh; (Houston,
TX) ; Jacobi; David; (Spring, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
|
SA |
|
|
Family ID: |
59091663 |
Appl. No.: |
15/190687 |
Filed: |
June 23, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 30/20 20200101;
E21B 43/24 20130101; E21B 41/0092 20130101; C09K 8/62 20130101;
G06Q 30/0201 20130101; E21B 43/267 20130101; E21B 49/00 20130101;
G01V 99/005 20130101; E21B 43/26 20130101 |
International
Class: |
E21B 43/26 20060101
E21B043/26; G06F 17/50 20060101 G06F017/50; G01V 99/00 20090101
G01V099/00; E21B 43/24 20060101 E21B043/24; G06Q 30/02 20120101
G06Q030/02; E21B 41/00 20060101 E21B041/00 |
Claims
1. A method for treating a geologic formation, comprising:
providing a hydraulic fracture model; providing a first value
representative of a volume of kerogen breaker in a fracturing
fluid; determining a discrete fracture network (DFN) based on the
hydraulic fracture model and the first value; determining a
geomechanical model based on the DFN and a reservoir model based on
the DFN; determining a hydrocarbon production volume based on the
geomechanical model and the reservoir model; adjusting the first
value based on the hydrocarbon production volume; and adjusting a
volume of kerogen breaker in the fracturing fluid to a hydrocarbon
reservoir based on the adjusted first value.
2. The method of claim 1, further comprising: providing a second
value representative of an amount of heat to apply to the
hydrocarbon reservoir; adjusting the second value based on the
hydrocarbon production volume; wherein, determining the DFN is
further based on the second value; and adjusting the amount of heat
to apply to the hydrocarbon reservoir is further based on the
adjusted second value.
3. The method of claim 2, wherein the amount of heat has a heating
cost, the hydrocarbon production volume has a market value, and
adjusting the second value comprises determining a difference
between the market value and the heating cost and adjusting the
second value to increase the difference.
4. The method of claim 2, further comprising extracting a volume of
hydrocarbon from the hydrocarbon reservoir based on the volume of
kerogen breaker in the fracturing fluid, and adjusting the second
value based on the extracted volume.
5. The method of claim 1, wherein the volume of kerogen breaker in
the fracturing fluid has a material cost, the hydrocarbon
production volume has a market value, and adjusting the first value
comprises determining a difference between the market value and the
material cost and adjusting the first value to increase the
difference.
6. The method of claim 1, wherein the DFN is descriptive of one or
more of new fractures that are predicted to be created based on the
hydraulic fracturing model, modified shale properties predicted to
be modified based on the hydraulic fracturing model, and
reactivated fractures that are predicted to be reactivated based on
the hydraulic fracturing model and the modified shale
properties.
7. The method of claim 1, wherein the hydraulic fracture model is
configured to determine the DFN further based on one or more of
in-situ stresses in the reservoir field, pore pressures in the
reservoir field, injection plans of a fracturing job, heterogeneity
in the reservoir formation, elastic stiffness properties of
reservoir rocks, plastic strength properties of reservoir rocks,
and mechanical properties of heterogeneities, and the DFN comprises
a number of fractures each characterized by one or more of fracture
length, fracture width, fracture height, and fracture
orientation.
8. The method of claim 1, wherein the geomechanical model is
configured to predict the evolution of at least one of stress
fields, deformation, and damage in the reservoir based on one or
more of in-situ stresses in the reservoir field, pore pressures in
the reservoir field, rock masses of reservoir layers, the DFN,
constitutive models of rock mass that describe
stress-deformation-failure processes of reservoirs under loading
modes, mechanical properties of rock masses, mechanical properties
of fractures, fluid mechanical interaction parameters, and thermal
mechanical coupling parameters.
9. The method of claim 1, wherein the reservoir model is configured
to predict the evolution of multiphase flow and pressure fields in
the reservoir based on one or more of reservoir pressure
distribution parameters, reservoir temperature distribution
parameters, multiphase flow models for fluid flow in rock,
multiphase flow models for fluid flow in the DFN, thermal
conduction models, thermal convection models, porosity parameters,
permeability parameters, saturation parameters, thermal conduction
property parameters, thermal convection property parameters, well
location parameters, well drawdown plan parameters, and well
temperature parameters.
10. The method of claim 1, further comprising extracting a volume
of hydrocarbon from the hydrocarbon reservoir based on the volume
of kerogen breaker in the fracturing fluid, and adjusting the first
value based on the extracted volume.
11. A system for hydraulic fracturing comprising: a hydraulic
fracture model configured to determine a discrete fracture network
(DFN) based on a first value representative of a volume of kerogen
breaker in a fracturing fluid; a geomechanical model based on the
DFN and a reservoir model based on the DFN, the geomechanical model
and the reservoir model configured to determine a hydrocarbon
production volume; and an adjustment module configured to adjust
the first value based on the hydrocarbon production volume.
12. The system of claim 11, further comprising a valve configured
to adjust a volume of kerogen breaker in the fracturing fluid to a
hydrocarbon reservoir based on the adjusted first value.
13. The system of claim 11, wherein: the hydraulic fracture model
is configured to determine the discrete fracture network (DFN)
further based on a second value representative of an amount of heat
to apply to the hydrocarbon reservoir; and the adjustment module is
further configured to adjust the second value based on the
hydrocarbon production volume.
14. The system of claim 13, wherein the amount of heat has a
heating cost, the hydrocarbon production volume has a market value,
and the adjustment model is further configured to adjust the second
value based on determining a difference between the market value
and the heating cost and adjusting the second value to increase the
difference.
15. The system of claim 13, further comprising a valve configured
to adjust delivery of heat provided to a hydrocarbon reservoir
based on the adjusted second value.
16. The system of claim 11, wherein the volume of kerogen breaker
in the fracturing fluid has a material cost, the hydrocarbon
production volume has a market value, and the adjustment model is
further configured to adjust the second value based on determining
a difference between the market value and the material cost and
adjusting the first value to increase the difference.
17. The system of claim 11, wherein the DFN is descriptive of one
or more of new fractures that are predicted to be created based on
the hydraulic fracturing model, modified shale properties predicted
to be modified based on the hydraulic fracturing model, and
reactivated fractures that are predicted to be reactivated based on
the hydraulic fracturing model and the modified shale
properties.
18. The system of claim 11, wherein the hydraulic fracture model is
configured to determine the DFN further based on one or more of
in-situ stresses in the reservoir field, pore pressures in the
reservoir field, injection plans of a fracturing job, heterogeneity
in the reservoir formation, elastic stiffness properties of
reservoir rocks, plastic strength properties of reservoir rocks,
and mechanical properties of heterogeneities, and the DFN comprises
a number of fractures each characterized by one or more of fracture
length, fracture width, fracture height, and fracture
orientation.
19. The system of claim 11, wherein the geomechanical model is
configured to predict the evolution of at least one of stress
fields, deformation, and damage in the reservoir based on one or
more of in-situ stresses in the reservoir field, pore pressures in
the reservoir field, rock masses of reservoir layers, the DFN,
constitutive models of rock mass that describe
stress-deformation-failure processes of reservoirs under loading
modes, mechanical properties of rock masses, mechanical properties
of fractures, fluid mechanical interaction parameters, and thermal
mechanical coupling parameters.
20. The system of claim 11, wherein the reservoir model is
configured to predict the evolution of multiphase flow and pressure
fields in the reservoir based on one or more of reservoir pressure
distribution parameters, reservoir temperature distribution
parameters, multiphase flow models for fluid flow in rock,
multiphase flow models for fluid flow in the DFN, thermal
conduction models, thermal convection models, porosity parameters,
permeability parameters, saturation parameters, thermal conduction
property parameters, thermal convection property parameters, well
location parameters, well drawdown plan parameters, and well
temperature parameters.
Description
TECHNICAL FIELD
[0001] This disclosure relates to the adjustment of quantities of
hydraulic fracturing agents provided to kerogen-rich reservoirs for
hydrocarbon extraction.
BACKGROUND
[0002] In some instances, a geologic formation, such as shale, may
be fractured to initiate or enhance hydrocarbon production from the
formation. Fracturing typically involves pumping a fluid into a
wellbore at a particular pressure to break, or "fracture," the
geologic formation. The hydrocarbon fluid may then flow through the
fractures and cracks generated by the fracturing process to the
wellbore, and ultimately to the surface. In some instances, the
fracturing process includes multiple stages of high-pressure fluid
circulation into the wellbore, which may involve increased costs
and complexities.
SUMMARY
[0003] In general, this document describes the use of hydraulic
fracturing agents for hydrocarbon extraction in kerogen-rich
unconventional formations.
[0004] In a first aspect, a method for treating a geologic
formation includes providing a hydraulic fracture model, providing
a first value representative of a volume of kerogen breaker in a
fracturing fluid, determining a discrete fracture network (DFN)
based on the hydraulic fracture model and the first value,
determining a geomechanical model based on the DFN and a reservoir
model based on the DFN, determining a hydrocarbon production volume
based on the geomechanical model and the reservoir model, adjusting
the first value based on the hydrocarbon production volume, and
adjusting a volume of kerogen breaker in the fracturing fluid to a
hydrocarbon reservoir based on the adjusted first value.
[0005] Various implementations can include some, all, or none of
the following features. The method can further include providing a
second value representative of an amount of heat to apply to the
hydrocarbon reservoir, adjusting the second value based on the
hydrocarbon production volume, wherein, determining the DFN can be
further based on the second value, and adjusting the amount of heat
to apply to the hydrocarbon reservoir is further based on the
adjusted second value. The amount of heat can have a heating cost,
the hydrocarbon production volume can have a market value, and
adjusting the second value can include determining a difference
between the market value and the heating cost and adjusting the
second value to increase the difference. The method can further
include extracting a volume of hydrocarbon from the hydrocarbon
reservoir based on the volume of kerogen breaker in the fracturing
fluid, and adjusting the second value based on the extracted
volume. The volume of kerogen breaker in the fracturing fluid can
have a material cost, the hydrocarbon production volume can have a
market value, and adjusting the first value can include determining
a difference between the market value and the material cost and
adjusting the first value to increase the difference. The DFN can
be descriptive of one or more of new fractures that are predicted
to be created based on the hydraulic fracturing model, modified
shale properties predicted to be modified based on the hydraulic
fracturing model, and reactivated fractures that are predicted to
be reactivated based on the hydraulic fracturing model and the
modified shale properties. The hydraulic fracture model can be
configured to determine the DFN further based on one or more of
in-situ stresses in the reservoir field, pore pressures in the
reservoir field, injection plans of a fracturing job, heterogeneity
in the reservoir formation, elastic stiffness properties of
reservoir rocks, plastic strength properties of reservoir rocks,
and mechanical properties of heterogeneities, and the DFN can
include a number of fractures each characterized by one or more of
fracture length, fracture width, fracture height, and fracture
orientation. The geomechanical model can be configured to predict
the evolution of at least one of stress fields, deformation, and
damage in the reservoir based on one or more of in-situ stresses in
the reservoir field, pore pressures in the reservoir field, rock
masses of reservoir layers, the DFN, constitutive models of rock
mass that describe stress-deformation-failure processes of
reservoirs under loading modes, mechanical properties of rock
masses, mechanical properties of fractures, fluid mechanical
interaction parameters, and thermal mechanical coupling parameters.
The reservoir model can be configured to predict the evolution of
multiphase flow and pressure fields in the reservoir based on one
or more of reservoir pressure distribution parameters, reservoir
temperature distribution parameters, multiphase flow models for
fluid flow in rock, multiphase flow models for fluid flow in the
DFN, thermal conduction models, thermal convection models, porosity
parameters, permeability parameters, saturation parameters, thermal
conduction property parameters, thermal convection property
parameters, well location parameters, well drawdown plan
parameters, and well temperature parameters. The method can also
include extracting a volume of hydrocarbon from the hydrocarbon
reservoir based on the volume of kerogen breaker in the fracturing
fluid, and adjusting the first value based on the extracted
volume.
[0006] In a second aspect, a system for hydraulic fracturing
includes a hydraulic fracture model configured to determine a
discrete fracture network (DFN) based on a first value
representative of a volume of kerogen breaker in a fracturing
fluid, a geomechanical model based on the DFN and a reservoir model
based on the DFN, the geomechanical model and the reservoir model
configured to determine a hydrocarbon production volume, and an
adjustment module configured to adjust the first value based on the
hydrocarbon production volume.
[0007] Various implementations can include some, all, or none of
the following features. The system can also include a valve
configured to adjust a volume of kerogen breaker in the fracturing
fluid to a hydrocarbon reservoir based on the adjusted first value.
The hydraulic fracture model can be configured to determine the
discrete fracture network (DFN) further based on a second value
representative of an amount of heat to apply to the hydrocarbon
reservoir, and the adjustment module can be further configured to
adjust the second value based on the hydrocarbon production volume.
The amount of heat can have a heating cost, the hydrocarbon
production volume can have a market value, and the adjustment model
can be further configured to adjust the second value based on
determining a difference between the market value and the heating
cost and adjusting the second value to increase the difference. The
system can also include a valve configured to adjust delivery of
heat provided to a hydrocarbon reservoir based on the adjusted
second value. The volume of kerogen breaker in the fracturing fluid
can have a material cost, the hydrocarbon production volume can
have a market value, and the adjustment model can be further
configured to adjust the second value based on determining a
difference between the market value and the material cost and
adjusting the first value to increase the difference. The DFN can
be descriptive of one or more of new fractures that are predicted
to be created based on the hydraulic fracturing model, modified
shale properties predicted to be modified based on the hydraulic
fracturing model, and reactivated fractures that are predicted to
be reactivated based on the hydraulic fracturing model and the
modified shale properties. The hydraulic fracture model can be
configured to determine the DFN further based on one or more of
in-situ stresses in the reservoir field, pore pressures in the
reservoir field, injection plans of a fracturing job, heterogeneity
in the reservoir formation, elastic stiffness properties of
reservoir rocks, plastic strength properties of reservoir rocks,
and mechanical properties of heterogeneities, and the DFN can
include a number of fractures each characterized by one or more of
fracture length, fracture width, fracture height, and fracture
orientation. The geomechanical model can be configured to predict
the evolution of at least one of stress fields, deformation, and
damage in the reservoir based on one or more of in-situ stresses in
the reservoir field, pore pressures in the reservoir field, rock
masses of reservoir layers, the DFN, constitutive models of rock
mass that describe stress-deformation-failure processes of
reservoirs under loading modes, mechanical properties of rock
masses, mechanical properties of fractures, fluid mechanical
interaction parameters, and thermal mechanical coupling parameters.
The reservoir model can be configured to predict the evolution of
multiphase flow and pressure fields in the reservoir based on one
or more of reservoir pressure distribution parameters, reservoir
temperature distribution parameters, multiphase flow models for
fluid flow in rock, multiphase flow models for fluid flow in the
DFN, thermal conduction models, thermal convection models, porosity
parameters, permeability parameters, saturation parameters, thermal
conduction property parameters, thermal convection property
parameters, well location parameters, well drawdown plan
parameters, and well temperature parameters.
[0008] The systems and techniques described here may provide one or
more of the following advantages. First, a system can identify
amounts of kerogen-reducing or removing agents that have
corresponding estimates for volumes of extracted hydrocarbons.
Second, the system can increase the efficiency of extracting
volumes of hydrocarbons based on predetermined amounts of
kerogen-reducing agents to be used. Third, the system can increase
the profitability of hydrocarbon extraction processes in
kerogen-rich formations where kerogen-reducing agents are in
use.
[0009] The details of one or more implementations are set forth in
the accompanying drawings and the description below. Other features
and advantages will be apparent from the description and drawings,
and from the claims.
DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a schematic diagram of an example of a well
system.
[0011] FIG. 2 is a schematic diagram that shows an example of a
control system.
[0012] FIG. 3 is flow chart that shows an example of a process for
adjusting kerogen breaker volume values.
DETAILED DESCRIPTION
[0013] FIG. 1 is a schematic diagram of an example well system 10.
The well system 10 includes a fracturing device 45, through which
kerogen breaker in fracturing fluids or heat or both may be applied
on a hydrocarbon production field such as a rock formation 42 of a
kerogen-rich, unconventional subterranean zone 40.
[0014] In some instances, in the kerogen-rich shales, the extensive
existence of kerogen may have significant influence upon the
overall mechanical behavior of the shales. However, due to the
micro- or nano-scale of some kerogen volumes, it is impractical to
measure the mechanical properties and behaviors of kerogen in
conventional geomechanics testing configurations, such as a
uniaxial test, a triaxial test, or a Brazilian disc test.
[0015] Generally speaking, kerogens can demonstrate
strain-softening, ductile mechanical behavior when subjected to
tensile load. An implication of this observation is that kerogen
can have a negative impact on the initiation and propagation of
fractures and sustainability of fracture opening in kerogen-rich
unconventional reservoir formations. In some implementations, these
negative impacts can be reduced by adding breaker, heat, or other
treatments in the fracturing fluids. The dose of breaker, for
example, can determined by the tradeoff between the cost of adding
breakers into fracturing fluids and the value of the resulting
increase in hydrocarbon (for example, petrochemical, oil)
production. In some implementations, the amount of treatment can be
determined by a recursive numerical simulation, which takes stress,
pressure and mechanical properties of reservoir formation,
including kerogen domains, and fracturing fluid properties as
inputs and can predict the fracture extension, sustainability, and
productivity of the stimulated reservoir. In some implementations,
the amount of treatment can be determined in real time by feedback
control process, which takes target and actual hydrocarbon
extraction rates as inputs and can adjust the amount of treatment
to approach the target extraction rate. In some implementations,
the feedback control process can take a market value for
hydrocarbons and the costs of treatments as inputs, and can adjust
the amount of treatment to adjust a net financial gain.
[0016] The fracturing compounds, in some implementations, may
decompose or remove at least part of the kerogen domains in the
rock formation 42. For example, exposure of the rock formation 42
to breaker compounds or heat or both can at least partly dissolve
kerogen, easing the flow of hydrocarbons through the rock formation
42 to a wellbore 20.
[0017] As shown, the well system 10 accesses a subterranean zone 40
(which can be a formation, a portion of a formation or multiple
formations), and provides access to hydrocarbons located in such
subterranean zone 40. In an example implementation of system 10,
the system 10 can be used for a drilling operation in which a
downhole tool 50 can include or be coupled with a drilling bit. In
another example implementation of system 10, the system 10 can be
used for a completion, for example, hydraulic fracturing, operation
in which the downhole tool 50 can include or be coupled with a
hydraulic fracturing tool. Thus, the well system 10 can allow for a
drilling or fracturing or stimulation operations.
[0018] The well system 10 also includes a control system 19, for
example, microprocessor-based, electro-mechanical, or otherwise,
that can determine or control the amount of breaker compound(s),
heat, or both to be applied downhole to fracture the kerogens in
the rock formation 42.
[0019] In hydraulic fracturing implementations, the bottom hole
pressures used to initiate fractures around the wellbore 20 are
called breakdown pressure (P.sub.b). For impermeable rock P.sub.b
can be related to in-situ stress and reservoir rock tensile
strength, and can be expressed as:
P.sub.b=3.sigma..sub.min-.sigma..sub.max+.sigma..sup.T
[0020] where .sigma..sub.max and .sigma..sub.min are maximum and
minimum in-situ effective principal stress, respectively;
.sigma..sup.T is the tensile strength of rock; P.sub.b is the
pressure above the initial in-situ pore pressure that is required
to break down the formation.
[0021] In some kerogen rich shales (KRS), the kerogen fibers can be
fine but can exist across large volumes. Their presence can be
described by widespread distributed "spider webs". The densely
distributed kerogens can have various implications upon hydraulic
fracturing. For example, kerogen can add extra strength to the
reservoir rock, so KRS can have higher tensile strength than
kerogen free shale (KFS), which can result in a higher breakdown
pressure being needed to initiate the fracture in KRS. In another
example, kerogen can have relatively high tensile strength at high
tensile deformation, which can raise fracture propagation pressure
to a higher pressure level than fracturing KFS in which the tensile
strength usually drops to zero quickly after the initial fracture.
In yet another example, after the proppants are placed in the
fractures and the bottom hole pressured decreased, the kerogen can
bounce back thereby imposing additional confining compressive
stress to the proppants in addition to the in-situ stress of
reservoir formation, which can cause additional embedment of
proppants into the formation resulting in extra reduction of the
fracture aperture.
[0022] Kerogen has negative impact on initiation and propagation of
fractures, and the sustainability of fracture opening in
kerogen-rich unconventional reservoir formations; fracturing fluid
shall reverse the negative effect of elastic rebound of kerogen
after the initial fracturing opening, including (1) use breaker to
decompose, at least partially, or (2) use other materials or
methods, to remove at least part of kerogen domains.
[0023] In the oilfield, commonly used oxidizers can include
persulfate, bromate, H.sub.2O.sub.2, H.sub.2O.sub.2-urea, and
H.sub.2O.sub.2-carbonate complexes. Cl-contained oxidizers can be
used as well. In some implementations, persulfate or bromate or
both can be good enough to remove all or part of kerogen. In some
implementations, iron (Fe) in kerogen can act as a catalyst to
speed up reactions. In some implementations, the FeS.sub.2 in
pyrite can be oxidized to release Fe ions.
[0024] Two series of tests, each consisting of four tests, were
conducted to break kerogen under laboratory conditions. In the
first series of tests, the same amount of breaker compound was used
to break the same amount of kerogen, but the breaking time was
different in each test. In the second series tests, different
amounts of breaker compound was used to break the same amount of
kerogen with same breaking times.
[0025] In the first series of tests, about 50 mg of kerogen and 500
mg of sodium bromate were added to 20 ml of deionized water in each
sample, and placed in a 300 F bath for 8, 16, 32, and 64 hours,
respectively. The residue was filtered out, dried, and weighed. The
tests show that this type of treatment can be useful to at least
partly remove kerogen.
[0026] The testing conditions and results are provided in Table
1.
TABLE-US-00001 TABLE 1 Weight reduction of kerogen with same amount
of sodium bromate (500 mg) but different time. Hours at Kerogen
initial Residue Weight 300 F. (hours) weight (mg) weight (mg)
reduction (%) 8 48.0 22 54 16 49.1 11 78 32 48.8 7 86 64 49.7 7
86
[0027] In the second series of test, around 50 mg of kerogen and
50, 100, 200, or 400 mg, respectively, of sodium bromate were added
to 20 ml of deionized water in each sample, and placed in a 300 F
bath for 48 hours. The residue was filtered out, dried, and
weighed. The testing conditions and results are presented in Table
2.
TABLE-US-00002 TABLE 2 Weight reduction of kerogen with different
amount of sodium bromate but same time (48 hours). NaBrO3 Kerogen
initial Residue Weight weight (mg) weight (mg) weight (mg)
reduction (%) 50.0 50.3 35 30 99.8 50.5 29 43 200.1 50.8 18 65
400.8 50.9 7 86
[0028] In the first series of tests, .about.500 mg of NaBrO.sub.3
caused a kerogen weight reduction of about 86% after sufficient
time. So it appears that about 400-500 mg of NaBrO.sub.3 can be
used to break about 50 mg of kerogen. In some implementations, it
may not be necessary to break down 100% of the organic materials in
kerogen. For example, as long as kerogen is weakened to such an
extent that it will not significantly affect fracture initiation
and propagation, the treatment can be considered to be
sufficient.
[0029] FIG. 2 is a schematic diagram that shows an example of a
control system 200. In some embodiments, the control system 200 can
be implemented by the example control system 19 of FIG. 1. As
discussed above, kerogen can be at least partly dissolved by
chemical means, depending on the amount of breaker (for example,
sodium bromate) and treatment time used. However, undertaking such
a pre-treatment operation, the time required to perform the
operation, and the volume of the breaker material used to perform
the operation can add extra cost to the process of extracting
hydrocarbons when compared with hydraulic fracturing processes
without such pre-treatment. On the other hand, in some
implementations, removal or reduction of kerogen domains along the
fractures can generate longer and wider fractures in hydraulic
fracturing, which can enhance well productivity. In some kerogen
treatment designs, the parameters of the pre-treatment operation
can be adjusted to increase the net financial gain from the kerogen
breaking treatment, based on the difference between the expense of
the operation (for example, cost of an amount of breaker compound
used) and the value of any additional hydrocarbon that can be
extracted as a result. The control system 200 is configured to
determine such pre-treatment parameters, apply them to the rock
zone 40 of FIG. 1, and estimate the effect upon the extraction of
hydrocarbons out of the wellbore 20.
[0030] The control system 200 implements a shale stiffness and
strength model 205. In some implementations, the model 205 can be
implemented as computer instructions stored on a computer-readable
medium and executable by one or more processors. Alternatively or
in addition, the model 205 can be implemented in hardware or
firmware or a combination of hardware, firmware and software. The
model 205 is configured to receive a kerogen breaker volume value
210 and determine a collection of modified shale formation
properties. In some implementations, the kerogen breaker volume
value 210 can be received from an external source, for example a
predetermined startup value provided by a storage system, a startup
value provided by a pseudorandom number generator, a value provided
by human operator, or any other appropriate source. The kerogen
breaker volume value 210 represents a quantity of a selected
breaker compound that is to be delivered down hole (for example, to
the rock formation 42). The shale stiffness and strength model 205
is configured to determine an amount by which a selected
kerogen-rich environment such as the rock formation 42 can be
affected by the application of a selected volume of kerogen
breaker. For example, shale stiffness and strength in the rock
formation 42 can be reduced by X % for a Y volume of kerogen
breaker. In some implementations, the collection of modified shale
formation properties can represent the estimated stiffness and
strength of shale in the selected kerogen-rich environment as a
result of providing the volume of kerogen breaker represented by
the kerogen breaker volume value 210.
[0031] The shale stiffness and strength model 205 is also
configured to receive a bottom hole heat up value 212 to determine
the collection of modified shale formation properties. In some
implementations, the bottom hole heat up value 212 can be received
from an external source, for example a predetermined startup value
provided by a storage system, a startup value provided by a
pseudorandom number generator, a value provided by human operator,
or any other appropriate source. The bottom hole heat up value 212
represents an amount of heat energy that is to be delivered down
hole (for example, to the rock formation 42). For example, a
temperature rise of 50.degree. C. can be selected to at least
partly dissipate kerogens. In some implementations, the heat energy
can be provided chemically. For example, an acid and a base can
both be delivered down hole, and the resulting reaction can create
heat that can dissipate kerogen. In some implementations, the heat
energy can be provided electrically. For example, microwave or
radio frequency energy can be delivered downhole to heat the rock
formation 42. In some implementations, other heating techniques can
be used (for example, steam, radiation, vibration, ultrasound,
lasers). The shale stiffness and strength model 205 is configured
determine an amount by which a selected kerogen-rich environment
such as the rock formation 42 can be affected by the application of
a selected amount of heat delivered down hole. For example, shale
stiffness and strength in the rock formation 42 can be reduced by M
% for an N amount of heat energy or temperature rise. In some
implementations, the collection of modified shale formation
properties can represent the estimated stiffness and strength of
shale in the selected kerogen-rich environment as a result of
providing the amount of bottom hole heat up represented by the
bottom hole heat up value 212. Without adding breaker, due to the
hindrance of rubbery kerogen domains, the breakdown pressure
observed during hydraulic fracturing can be larger. However, in
examples in which breaker is added, kerogen domains can be at least
partially broken and the hindrance can be weakened, resulting in
smaller breakdown pressure values.
[0032] The collection of modified shale formation properties
determined by the shale stiffness and strength model 205 are
received by a hydraulic fracture model 220. In some
implementations, the model 220 can be implemented as computer
instructions stored on a computer-readable medium and executable by
one or more processors. Alternatively or in addition, the model 220
can be implemented in hardware or firmware or a combination of
hardware, firmware and software. In some implementations, the
hydraulic fracture model 220 can also be configured to receive
additional information about a well system such as the well system
10. For example, the hydraulic fracture model 220 can accept
information including in-situ stresses and pore pressure in the
reservoir field, injection plans for a fracturing job,
heterogeneity in the reservoir formation, elastic stiffness
properties of reservoir rocks, plastic strength properties of
reservoir rocks, and mechanical properties of heterogeneities. In
some implementations, some of these properties can be measured in a
rock mechanics lab and provided for use by the hydraulic fracture
model 220.
[0033] The hydraulic fracture model 220 simulates a main hydraulic
fracturing stimulation based on the collection of modified shale
formation properties. In the simulation performed by the hydraulic
fracture model 220, some existing natural fractures can be
reactivated, new fractures can be created, and proppants can be
placed in the created fractures. As a result of this simulation, a
stimulated reservoir volume (SRV) consisting of new fractures or
reactivated natural fractures (or both) will be determined. The
output of hydraulic fracture model 220 is a discrete fracture
network (DFN) consisting of a description of a number of fractures,
wherein each fracture can be characterized by length, width,
height, and orientation.
[0034] The system 200 includes a geomechanical model 230. In some
implementations, the model 230 can be implemented as computer
instructions stored on a computer-readable medium and executable by
one or more processors. Alternatively or in addition, the model 230
can be implemented in hardware or firmware or a combination of
hardware, firmware and software.
[0035] The geomechanical model 230 is configured to receive the DFN
and estimate an amount of hydrocarbon production that the rock
formation 42 can provide based on the DFN. In some implementations,
the geomechanical model 230 can be configured to receive additional
information about a well system such as the well system 10. For
example, the geomechanical model 230 can accept information
including in-situ stresses and pore pressure in the reservoir
field, rock mass of reservoir layers, constitutive models of rock
mass that describe the stress-deformation-failure process of
reservoir under various loading modes, mechanical properties of
rock mass, mechanical properties of fractures, fluid mechanical
interaction parameters, and thermal mechanical coupling parameters.
In some implementations, some of these properties can be measured
in a rock mechanics lab and provided for use by the geomechanical
model 230.
[0036] The system 200 includes a reservoir model 232. In some
implementations, the model 232 can be implemented as computer
instructions stored on a computer-readable medium and executable by
one or more processors. Alternatively or in addition, the model 232
can be implemented in hardware or firmware or a combination of
hardware, firmware and software.
[0037] The reservoir model 232 is configured to receive the DFN and
estimate an amount of hydrocarbon production that the rock
formation 42 can provide based on the DFN. In some implementations,
the reservoir model 232 can be configured to receive additional
information about a well system such as the well system 10. For
example, the reservoir model 232 can accept information including
initial reservoir pressure distribution information, reservoir
temperature distribution information, multiphase flow models for
fluid flow in rock, multiphase flow models for fluid flow in the
DFN, thermal conduction models, and convection models, rock
porosity, rock permeability, saturation levels, thermal conduction
properties of rock, convective properties of rock, well location,
drawdown plans, and temperature at the production well.
[0038] The geomechanical model 230 and the reservoir model 232 are
bidirectionally coupled to each other. For example, the reservoir
model 232 can be at least partly driven by a drawdown plan at the
well system 10. In examples such as this, after thermal and fluid
flow modeling is performed, updated pore pressure and temperature
parameters can be transferred from the reservoir model 232 to the
geomechanics model 230. In such examples the geomechanical modeling
can be performed to bring the system to equilibrium, then the
estimated deformation, mechanical damage, and failure in the rock
formation 42 can be used to estimate updated porosity and
permeability parameters, and the deformation of the DFN can be used
to estimate the updated aperture or other geometric parameters of
the DFN. In such examples, updated geometric or mechanical
properties (or both) of rock mass or the DFN (or both the rock mass
and the DFN) can then be transferred from the geomechanical model
230 to the reservoir model 232, and the reservoir model 232 can
perform further estimation based on these updated parameters.
[0039] The output of the reservoir model 232 and the geomechanical
model 230 is an estimated production value 240. As an example, the
following ideal "Darcy", steady state, radial flow equation can be
used to calculate the inflow performance of a fully penetrating,
damaged, vertical, open hole well in a homogeneous formation.
q w = 0.00708 kh ( p r - p w ) B .mu. [ ln ( r e r w ) + S ]
##EQU00001##
[0040] where q.sub.w is the well flow rate; k is permeability (mD);
h is the thickness of reservoir layer (ft); p.sub.r is the
reservoir pressure (psi); p.sub.wis the flowing bottom hole
pressure (psi); B is the formation volume factor; .mu. is the
viscosity of reservoir fluid (cp); r.sub.e is drainage radius (ft);
r.sub.w is the well radius (ft); S is the skin factor.
[0041] Shales are anitropic and heterogeneous, and the fluid flow
related parameters of shale, such as permeability, skin factor,
fluid viscosity, and any other appropriate parameter of shale fluid
flow, can all evolve dynamically with the stress state of the rock
matrix and fractures. For these types of complex systems, no
analytical solutions exist to predict the production rate. Instead,
a coupling of geomechanical models and reservoir models can be
implemented to make reliable predictions, in which the
geomechanical model is used to update the stress and pore pressure
based on the updated pore pressure in the reservoir model, while
the updated stress and pore pressure are used to update the
permeability and porosity of rock matrix (and aperture and pressure
distribution along fractures) in reservoir models to be used in the
next step of computation in reservoir model.
[0042] The estimated production value 240 represents an accumulated
production of hydrocarbon. An adjustment module 250 can then
determine an updated kerogen breaker volume value to be provided to
the shale stiffness and strength model 205 based on the kerogen
breaker volume value 210 and the estimated production value 240.
The adjustment module 250 can also determine an updated bottom hole
heat up value to be provided to the shale stiffness and strength
model 205 based on the bottom hole heat up value 212 and the
estimated production value 240.
[0043] In some implementations, the system 200 can be run multiple
times to approach a selected objective. For example, the adjustment
model can be configured to perform a sweep or search of various
kerogen breaker volume values 210 or bottom hole heat up values 212
or both to determine a range of resulting estimated production
values 240.
[0044] In some implementations, the resulting estimated production
values 240 can be analyzed to identify an estimated production
value 240 that approaches a target parameter. For example, the
estimated production value 240 having the highest estimated value
can be selected, and the kerogen breaker volume value 210 or bottom
hole heat up value 212 (or both) that corresponds to the selected
estimated production value 240 can be identified and used to
configure production in the well system 10.
[0045] The updated kerogen breaker volume value is also provided as
an input to a valve 260. The valve 260 is configured to receive
kerogen breaker volume values and control a flow of kerogen breaker
compound that is delivered to the rock formation 42. For example,
if the system 200 determines that 2000 L of a selected breaker is
to be delivered down hole, then the valve 260 can be operated to
provide 2000 L of the breaker to the rock formation 42.
[0046] In a similar manner, the updated bottom hole heat up value
is also provided as an input to a valve 262. The valve 262 is
configured to bottom hole heat up values and control an amount of
heat that is delivered to the rock formation 42. For example, if
the system 200 determines that the rock formation 42 is to be
raised 40.degree. F., then the valve 262 can be operated to provide
one or more volumes of heat-generating chemical reactants, steam,
or other agents corresponding to the identified heat rise to the
rock formation 42. In some embodiments, the valve 262 can be
replaced by an electrical or other control mechanism. For example,
an electrical switch or amplifier can be used to determine a
corresponding amount of electrical, RF, microwave, or other energy
to be provided to the rock formation 42. In another example, a
mechanical oscillator or other vibratory mechanism (for example,
ultrasound or extremely low frequency--ELF--sound) can be used to
create heat energy down hole.
[0047] In some implementations, the breaker compound can have an
associated material cost (for example, a per-volume unit cost), and
a kerogen breaker compound cost can be determined based on the
material cost and the kerogen breaker volume value 210. For
example, if a selected breaker compound cost $0.10 per liter and
the kerogen breaker volume value represented 1000 liters, then the
kerogen breaker compound cost would be $100.
[0048] In some examples where the bottom hole heat up is provided
chemically, the chemical reactants used can have an associated
per-unit heating cost (for example, a per unit volumetric cost of
the reactants), and a heating cost can be determined based on the
per-unit heating cost and the bottom hole heat up value 212. For
example, it may be known that 1000 liters of a selected acid and
500 liters of a selected base cost $0.25/liter each, and therefore
a 20.degree. C. rise may consume (1000+500)*20=30000 liters of
reactants and have a heating cost of 3000010.25=$7500.
[0049] In some examples where the bottom hole heat up is provided
electrically, the electrical power can have an associated per-unit
heating cost (for example, a per kilowatt cost for electricity),
and the heating cost can be determined based on the per-unit
heating cost on the bottom hole heat up value 212. In some
implementations, other heating techniques can be used (for example,
steam, radiation, vibration, ultrasound, extreme low
frequency--ELF, lasers), and each heating technique can have its
own per-unit heating cost that can be used along with the bottom
hole heat up value 212 to determine the heating cost.
[0050] In some implementations, the system 200 can be configured to
identify values for the kerogen breaker volume value 210 or the
bottom hole heat up value 212 or both based on the per-unit costs
of the kerogen breaker compound, heating costs, and the per-unit
value of the estimated production 240. For example, the adjustment
module 250 can be configured to identify an estimated production
value 240 that approaches a maximized difference (for example,
profit margin) between the value of the estimated production value
240 and the costs of heating and the volumes of kerogen breaker
compound described by the kerogen breaker volume value 210 or the
bottom hole heat up value 212 or both corresponding to the
identified estimated production value 240.
[0051] FIG. 3 is flow chart that shows an example of a process 300
for adjusting kerogen breaker volume values. In some
implementations, the process 300 can be performed at least in part
by the example system 19 of the example well system 10 of FIG. 1 or
by the example system 200 of FIG. 2.
[0052] In the process 300, a hydraulic fracture model is provided.
In some implementations, the hydraulic fracture model can be the
example hydraulic fracture model 220. In some implementations, the
hydraulic fracture model can be configured to determine the
discrete fracture network (DFN) further based on a second value
representative of an amount of heat to apply to a hydrocarbon
reservoir, such as the rock formation 42. In some implementations,
the hydraulic fracture model can be configured to determine the DFN
further based on one or more of in-situ stresses in the reservoir
field, pore pressures in the reservoir field, injection plans of a
fracturing job, heterogeneity in the reservoir formation, elastic
stiffness properties of reservoir rocks, plastic strength
properties of reservoir rocks, and mechanical properties of
heterogeneities.
[0053] At 320 a first value is provided. The first value is
representative of a volume of kerogen breaker in fracturing fluid.
In some implementations, the first value can be the example kerogen
breaker volume value 210.
[0054] At 330 a discrete fracture network (DFN) is determined. The
example, the DFN is based on the hydraulic fracture model and the
first value. For example, the example hydraulic fracture model 220
simulates a main hydraulic fracturing stimulation based on the
collection of modified shale formation properties, and the output
of the hydraulic fracture model 220 is a DFN consisting of a
description of a number of fractures, wherein each fracture can be
characterized by one or more of length, width, height, and
orientation. In some implementations, the DFN can be descriptive of
one or more of new fractures that are predicted to be created based
on the hydraulic fracturing model, modified shale properties
predicted to be modified based on the hydraulic fracturing model,
and reactivated fractures that are predicted to be reactivated
based on the hydraulic fracturing model and the modified shale
properties.
[0055] At 340 a geomechanical model is determined. The
geomechanical model is determined based on the DFN. For example,
the geomechanical model can be the example geomechanical model 230.
The geomechanical model is configured to receive the DFN and
estimate an amount of hydrocarbon production that the rock
formation 42 can provide based on the DFN. In some implementations,
the geomechanical model can be configured to predict the evolution
of at least one of stress fields, deformation, and damage in the
reservoir based on one or more of in-situ stresses in the reservoir
field, pore pressures in the reservoir field, rock masses of
reservoir layers, the DFN, constitutive models of rock mass that
describe stress-deformation-failure processes of reservoirs under
loading modes, mechanical properties of rock masses, mechanical
properties of fractures, fluid mechanical interaction parameters,
and thermal mechanical coupling parameters.
[0056] At 350 a reservoir model is determined. The reservoir model
is based on the DFN. For example, the reservoir model can be the
example reservoir model 232. The reservoir model is configured to
receive the DFN and estimate an amount of hydrocarbon production
that the rock formation 42 can provide based on the DFN.
[0057] At 360, a hydrocarbon production volume is determined. The
hydrocarbon production volume is an estimate based on the amounts
of hydrocarbon production estimated by the geomechanical model and
the reservoir model for the given first value. In some
implementations, the hydrocarbon production volume can be the
example estimated production value 240. In some implementations,
the reservoir model can be configured to predict the evolution of
multiphase flow and pressure fields in the reservoir based on one
or more of reservoir pressure distribution parameters, reservoir
temperature distribution parameters, multiphase flow models for
fluid flow in rock, multiphase flow models for fluid flow in the
DFN, thermal conduction models, thermal convection models, porosity
parameters, permeability parameters, saturation parameters, thermal
conduction property parameters, thermal convection property
parameters, well location parameters, well drawdown plan
parameters, and well temperature parameters.
[0058] At 370, the first value is adjusted based on the determined
hydrocarbon production volume. In some implementations the first
value can be adjusted by the example adjustment module 250. For
example, the first value can be raised or lowered to effect an
increase or decrease in the estimated production value 240.
[0059] In some implementations, the first value can have an
associated monetary cost (for example, the cost of kerogen breaker
compound) and the estimated hydrocarbon production value (for
example, the market price of crude oil) can have an associated
monetary value, and the first value can be adjusted to increase the
difference between the costs and resulting estimated value (for
example, increase net profit).
[0060] At 380, a flow of kerogen breaker in fracturing fluid to a
hydrocarbon reservoir is adjusted based on the adjusted first
value. For example, the example adjusted kerogen breaker volume
value 210 can be used as part of a control routine that directs the
operation of the example valve 260. In some implementations, the
flow of kerogen breaker in fracturing fluid to the rock formation
42 can be based on an adjusted first value that increases the
difference between the value of hydrocarbon expected to be
extracted by the well system 10 and cost of the amount of kerogen
breaker compound used as part of the extraction process.
[0061] In some implementations, the first value can be adjusted at
370 based on an actual hydrocarbon production volume. For example,
as the valve 260 is operated to control the volume of kerogen
breaker compound that is delivered to the rock formation 42, the
amount of hydrocarbons extracted from the rock formation 42 may not
be the exact amount predicted by the geomechanical model 230 and
the reservoir model 232. In such examples, the actual value of the
produced hydrocarbons can be greater or less than the value of the
estimated production volume, and the first value can be adjusted to
increase the difference between the costs and resulting actual
value (for example, increase net profit).
[0062] In some implementations, a second value representative of an
amount of heat to apply to the hydrocarbon reservoir can be
provided, the DFN can be determined based on the second value, the
second value can be adjusted based on the hydrocarbon production
volume, and the amount of heat to apply to the hydrocarbon
reservoir can be adjusted based on the adjusted second value. For
example, the example bottom hole heat up value 212 can represent an
amount of heat energy or heat-producing material that can be used
to dissipate an amount of kerogen and affect the amount of
hydrocarbon produced by the example well system 10.
[0063] In some implementations, the volume of kerogen breaker in
fracturing fluid can have a material cost, the hydrocarbon
production volume can have a market value, and adjusting the first
value can include determining a difference between the market value
and the material cost and adjusting the first value to increase the
difference. In some implementations, the amount of heat can have a
heating cost, the hydrocarbon production volume can have a market
value, and adjusting the second value can include determining a
difference between the market value and the heating cost and
adjusting the second value to increase the difference.
[0064] For example, the bottom hole heat up value 212 may indicate
that $10,000 worth of acid and base would need to be delivered down
hole to generate a predetermined amount of kerogen-dissipating
heat, and the kerogen breaker volume value 210 may indicate that
$5,000 worth of breaker compound would need to be delivered down
hole to chemically dissipate a predetermined about of kerogen, and
the estimated production value 240 can indicate that $100,000 worth
of hydrocarbons could be extracted as a result. This would result
in a $-10,000-$5,000+$100,000=$85,000 net gain. The system 200 can,
for example, adjust the kerogen breaker volume value 210 to
indicate that $6,000 worth of breaker compound could be used to
produce an estimated production value 240 having a worth of
$110,000, or a $94,000 net gain. In such an example, the system 200
can select the latter kerogen breaker volume value 210 over the
first because the latter value provides a greater net return on
investment in breaker compounds and heat than the former value (for
example, $94,000 versus $85,000, an additional $9,000 return on an
additional $1,000 investment).
[0065] In some implementations, the process 300 can include
extracting a volume of hydrocarbon from the hydrocarbon reservoir
based on the volume of kerogen breaker in fracturing fluid, and
adjusting the first value based on the extracted volume. In some
implementations, the process 300 can include extracting a volume of
hydrocarbon from the hydrocarbon reservoir based on the volume of
kerogen breaker in fracturing fluid, and adjust the second value
based on the extracted volume. For example, the well system 10 may
initially be configured to deliver the $5,000 worth of breaker
compound down hole, and extract $100,000 worth of hydrocarbon as a
result. The control system 200 can adjust the valve 260 to increase
the amount of breaker compound being delivered down hole and detect
that an additional amount of hydrocarbon is being produced from the
rock formation 42. In some implementations, the control system 200
can adjust the kerogen breaker volume value 210, the bottom hole
heat up value 212, or both, based on the increases and decreases in
the hydrocarbon volumes that can be extracted as a result, for
example, to improve production volumes or profit margins for the
amounts of hydrocarbon that can be extracted as a result.
[0066] A number of implementations have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
disclosure. For example, example operations, methods, or processes
described herein may include more steps or fewer steps than those
described. Further, the steps in such example operations, methods,
or processes may be performed in different successions than that
described or illustrated in the figures. As another example,
although certain implementations described herein may be applicable
to tubular systems (for example, drill pipe or coiled tubing),
implementations may also utilize other systems, such as wireline,
slickline, e-line, wired drill pipe, wired coiled tubing, and
otherwise, as appropriate. As another example, some criteria, such
as temperatures, pressures, and other numerical criteria are
described as within a particular range or about a particular value.
In some aspects, a criterion that is about a particular value is
within 5-10% of that particular value. Accordingly, other
implementations are within the scope of the following claims.
* * * * *